Exhaust emissions from motorized on-highway machines are regulated by the relevant government agencies and must not exceed certain contaminant levels. For example, some government regulations place limits on the amount, and maybe sizing, of particulate matter that may be emitted by diesel truck engines. Particulate matter may include, for example, carbon particulate, unburned hydrocarbons, and sulfates. Additional regulations may specify acceptable levels of gaseous emissions (e.g., NOx, CO) that may be part of the exhaust gas stream from the engine. Early regulations primarily addressed undesirable emission levels when the engine was operating in a relatively steady state condition. More recent regulations have been promulgated to regulate undesirable emissions when the engine is undergoing a transient condition, such as accelerating from one speed and load condition to another speed and load condition to another speed and load.
Due to these regulations, equipment has been developed to test and analyze machine engines and/or power sources for conformance with governmental standards. In particular, partial flow exhaust gas sampling systems have been developed in an effort to certify such power sources as being in compliance with government emissions regulations with regard to particulate matter. Generally, these systems operate by extracting a small portion of a power source's exhaust flow via a test probe located in the exhaust stack. A regulated flow of filtered ambient air is then mixed with the extracted portion, and the combined flow is directed to a filter configured to trap the particulate matter contained within the combined flow. The power source may then be evaluated based on the quantity of particulate matter trapped by the filter during a particular test cycle. Examples of such particulate sampling systems and methods that have performed well in recent years are shown and described in co-owned U.S. Pat. Nos. 6,615,677, 7,299,690, 7,404,340, 7,406,885 et al.
While these systems have shown the ability to perform well with regard to particulate matter assessments, there is a growing need to certify engines with regard to other undesirable emissions, including but not limited to particulate size and undesirable gaseous emissions including NOx and carbon monoxide. The alternative to partial flow systems might be a full dilution tunnel. However, these systems are extremely expensive and do not have the capability of testing a broad range of sizes of different diesel engines, and in fact do not have the capacity for some of the relatively large diesel engines that appear in some machines of the type manufactured by Caterpillar Inc. of Peoria Ill. Full dilution systems also face problems when attempting to perform simultaneous pre and post-after treatment sampling for system effectiveness studies, as the full-flow design of these systems makes such sampling physically impossible.
One potential solution to the problem of simultaneously evaluating exhaust emissions with two or more testing procedures could involve the usage of two or more partial flow dilution systems operating in parallel in one test cell. While such a solution may at first appear to be viable, the real estate available in a typical test cell may not allow for the associated hardware and computing equipment necessary to effectively operate two or more parallely arranged partial dilution sampling systems. On the other hand, incorporating an additional testing evaluation system, in addition to particulate matter weight systems typically associated with partial flow dilution systems, can also be problematic. In other words, the integrity of the particulate matter assessment relies heavily upon accurate measurement and control of exhaust sampling flow rates, residence time, dilution flow rates, flow velocity at the filter face, as well as assumptions associated with conservation of matter.
The systems and methods of the present disclosure are directed to overcome one or more of the problems set forth above.